1. Field of the Invention
This invention is related generally to lithographic systems and their method of use.
2. Related Art
A lithographic apparatus is a machine that applies a desired pattern onto a target portion of a substrate. Lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs), flat panel displays and other devices involving fine structures. In a conventional lithographic apparatus, a patterning means, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern corresponding to an individual layer of the IC (or other device), and this pattern can be imaged onto a target portion (e.g., comprising part of one or several dies) on a substrate (e.g., a silicon wafer or glass plate) that has a layer of radiation-sensitive material (resist). Instead of a mask, the patterning means may comprise an array of individually controllable elements that generate the circuit pattern on an impinging light beam.
In general, a single substrate will contain a network of adjacent target portions that are successively exposed. Lithographic apparatus include steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion in one pass, and scanners, in which each target portion is irradiated by scanning the pattern through the projection beam in a given direction (the “scanning”-direction), while synchronously scanning the substrate parallel or anti-parallel to this direction.
The area on a substrate to be exposed with a given pattern is typically significantly larger than a size of the patterned beam that is incident on the substrate at a given instant. Consequently, the exposure pattern on the substrate is broken down into smaller portions, corresponding to the size of the patterned beam projected onto the substrate. These portions are then successively projected onto the substrate.
The complete pattern to be exposed on the substrate is typically made up of repeating units. This is the case, for example, where a plurality of identical devices are to be formed on the substrate. In this case, the pattern for each device is a repeating unit.
The size of the repeating unit varies, depending on the device being formed. However, the size of the patterned field projected onto the substrate is fixed for each apparatus by the size of the array of individually controllable elements and the magnification of the projection system. Consequently, where the pattern for a first copy of a repeating unit is generated at a given location on the array of individually controllable elements, the same part of the pattern of the repeating unit is generally not generated at the same location for the second and third copies. This means that the data path for controlling the array of individually controllable elements and/or the data storage space required in the apparatus, and hence the cost of the apparatus, is greatly increased.
Therefore, what is needed is to reduce the complexities of providing the data to the array of individually controllable elements, regardless of the variations of the size of the repeating units of pattern to be exposed on the substrate.